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Blast420
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5287280 - 06/24/12 07:23 PM

It would cost me about $40-$100 to make a fiberglass tube in the 6” to 12” range up to about 6’ in length, thats not including the gelcoat which adds about another $10-$20.

Edited by Blast420 (06/24/12 07:23 PM)


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Mirzam
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5287980 - 06/25/12 07:56 AM

I know that some people have used these:

http://www.yazoomills.com/mailing-tubes/heavy-duty-kraft.aspx

JimC


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: Mirzam]
      #5288382 - 06/25/12 01:00 PM

That looks like the source for the blue paper tube I used to roll the thin plywood up in. I've left that tube outside in the rain, and although it started blistering at the bottom end, it dried out okay and is still fine.

Prices seem reasonable, too. But I think I'd want to use a low-viscosity epoxy to stiffen it and protect it some, like Abatron's liquid wood that I use for home repairs and stuff.

-Tim.


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Pinbout
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5288401 - 06/25/12 01:10 PM Attachment (33 downloads)

that yazoomills tube is what I used for my stellafane rip off...
still need to paint the tube in a catalyzed poly, that stuff can make bullets bounce off of it.


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: Pinbout]
      #5288578 - 06/25/12 03:04 PM

Good suggestion! Where do you get the catalyzed polyurethane?

-Tim.


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Pinbout
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5288767 - 06/25/12 04:53 PM

I use an automotive clear topcoat that has to be mixed 100 parts poly 50 parts hardener. the clear is a high solids.

I use sikkens paint they've changed their product name several times over the years.

this is similar, not the same but very similar.


http://www.ebay.com/itm/Qt-High-Gloss-2K-Acrylic-PolyUrethane-Urethane-Clear-Coat-Clearcoat-Paint-Kit-/271003558006?pt=Motors_Automotive_Tools&hash=item3f19122076&vxp=mtr


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: Pinbout]
      #5288914 - 06/25/12 06:31 PM

Wow, that's really reasonable!

How well would it penetrate the paper, I wonder?

-Tim.


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Pinbout
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5288988 - 06/25/12 07:33 PM

well I'm going to gel coat the tube as a primer with a typical lacquer primer and put a color base coat before I clear coat the tube.

I don't know about penetrating but it will adhere very well. you have to wait 24hours before you sand between coats with my sikkens.


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: Pinbout]
      #5296394 - 06/30/12 01:51 PM Attachment (31 downloads)

Okay, do over!!

I decided to continue this thread rather than start another one, as I'm not ashamed to admit when I've done something stupid or tried something that doesn't work...

So, I decided to use that 5.5' 2x6 of beautiful grain cherry that I bought about a year ago for a scope project. Since it's only 5 1/2 feet long, I plan to make a removable dewshield and/or a removable primary mirror box/cell, since the FL of the mirror is 72".

Also, since I had already made forms to roll plywood up inside that are 9 3/4" ID, I decided to use them to control the cylindricity of the faceted tube. HOWEVER, my traditional 9-sided tube won't work, since the insides of the facets would be too close to the optical path (about 0.06"). So, I played with the polygon calculator Poly and came up with a 20-sided tube with 1.5" sides as my best option.

Here are the sides, all cut up and thickness planed smooth. Next I'll trim them to width and bevel the edges. I could use a cooper's bit set that I have, but I think that would take longer to set up than simply angling the table saw blade.


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296404 - 06/30/12 01:58 PM Attachment (34 downloads)

The slats are all bookmatched, so the grain more or less continues from one slat to the next, but of course there will be missing gaps from the saw kerf when I cut the bevels and the slats to width.

Here are all the forms I made last week, plus some lazy susan bearings I bought online to make rotating rings (very reasonably priced, compared to "real" rotating rings from Parks or Parallax, but they'll need reinforcment rings of plywood to control flexure). The site where I got these doesn't list the ID for the larger sizes, only the OD. So, I was pleasantly surprised to find that they're maybe a millimeter under 9.75" ID.

The smaller ring is one that I added to the order to try for other things, and since it's about 3.5" ID, I think I might use it as part of a rotating focuser mechanism. I still haven't decided on my focsuer. Probably a sled (with the rotator incorporated, perhaps). But I've also been cogitating about building the mirror box something like a Clement focuser body, where the mirror cell is mounted to the moving part of the "focuser". Then, I could call my eyepiece holder a "no-profile focuser" or something! Of course, it'll have some profile. But I'm not sure how feasible it will be to make a moving primary cell that maintains alignment.

I'm not likely to finish this weekend anyway. But it'll be nice to lay up the tube at least.


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296411 - 06/30/12 02:01 PM

For putting the tube together, I was planning on doing something like I've always done - where I use a boatload of painter's masking tape to tape up the sides into a venetian blind, turn them over and squeeze glue into the grooves between slats, roll the whole thing up, and put it in the forms?

If I do it that way (or even if I lay one side in the forms at a time), I plan to cut one side of the forms so I can expand them to take the rolled up tube, then put clams across the gap and squeeze the tube together and hold it round while the glue dries.

Thoughts?

-Tim.


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296416 - 06/30/12 02:03 PM

Oh, and the lazy susan bearings were $15 for each of the big ones and under $8 for the small one.

-Tim.


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296420 - 06/30/12 02:04 PM

Back to work!

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Jeff Morgan
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296556 - 06/30/12 03:38 PM Attachment (35 downloads)

Just getting up to speed on your thread Tim. I'll bet your f/9 is going to be killer. When people try to pigeonhole these as "planetary" scopes, they're missing something very important - a scope that is great on planets will be great on anything!

As to the tube construction, I would also go strip plank, or possibly octagonal. The issue there being how accurately one can make long cuts at the required 22.5 degree angle. I wouldn't want any gaps in the joint over the length. (I have enough trouble making 45 degree miters work!) One possible approach to cover that would be to do a hardwood inlay down the length of the joint. I'm doing this on my current project. It uses very thin (1/16" plywood) which is next to impossible to get clean joints with. So I cut away the edges on a router table and laid in a mahogany strips and sanded it all flush (photo attached of the piece in progress - note the edges.)

I'm not familiar with Coopers bits - would you be referring to bead & cove router bits? I have seen articles on this before, it seems rather straightforward work on a router table. Tack the strips to your forms (or better yet, use contrasting hardwood dowels) which can double as light baffles.


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: Jeff Morgan]
      #5296586 - 06/30/12 03:59 PM Attachment (25 downloads)

Hi Jeff!

That looks pretty nice to me!

I've already cut all the bevels on the table saw. The chief reason for going with 20 sides is because I'd already made forms and the lazy susan bearings are just the right ID.

I just checked in my garage, and I need a LOT of painter's tape. So I think I'll make myself a sandwich and scarf some potato chips and head on over to Home Despot for a bunch of tape.

Fewer sides is better, from a truing standpoint. The steeper the angle, the better control on a straight tube.

I set up the forms on my 1960 VW singlecab pickup bed to see how things would go, but it's so hot and sunny right now that I think I'm going to have to do this on my garage floor.


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296590 - 06/30/12 04:01 PM Attachment (35 downloads)

I cut kerfs in each form so I can clamp them tight around the tube while it dries. Also, I can wedge a screwdriver in to get them off the finished tube...

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Wes James
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296656 - 06/30/12 04:57 PM

Tim-
You're on your way to an amazing scope!!! 8" of aperture capable of high powers- wow!! And we all know that DelMarva mirrors are tops- the quality goes without saying!! Enjoying the thread, anxious to see the finished produce! What are you planning on doing on the inside of the tube??? I've used Yazoo tubes before/successfully- primered them inside/outside with thinned Poly varnish- then used flat black paint with a bucketfull of sawdust inside- dumped it/let it dry/rolled another coat of flat black over that... gave a wonderfully darkened tube inside.


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: Wes James]
      #5296695 - 06/30/12 05:36 PM

I'm planning on poly inside and out, followed by Rustoleum flat black inside, which I've had good results with before. I may add sawdust to it as well. I've sure made plenty of it!

-Tim.


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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296831 - 06/30/12 07:26 PM Attachment (25 downloads)

Okay, started taping the sides together!

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tim53
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Re: Delmarvascopics 8" f/9 OTA build new [Re: tim53]
      #5296834 - 06/30/12 07:27 PM Attachment (29 downloads)

The trouble with having so many sides is that this method uses a LOT of tape. I think I went through about 2/3rds of a new roll:

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